In recent years, an interest in global environment problems has increased and an improvement in the energy efficiency has been required. As a measure against global environment problems, there exists a green wave driving assistance system that assists an optimal method of making a user drive through continuous signalized intersections on the basis of traffic light information acquired via road-to-vehicle communications, thereby preventing useless acceleration and deceleration of the vehicle and providing an improvement in the fuel efficiency.
A problem with a conventional system using road-to-vehicle communications is that because there is a necessity to place a huge number of roadside units each of which transmits traffic light information to vehicles in the surroundings of intersections, it is difficult to put this system to practical use.
As a technique for solving this problem, for example, patent reference 1 discloses a navigation device that generates a traffic signal database via a vehicle-mounted unit or a server by capturing the light color of a traffic light using a camera mounted in a vehicle and analyzing image data, and provides traffic signal guidance information.
Further, patent reference 2 discloses a vehicle-mounted device that guides a remaining time which will elapse until the light color of the traffic light changes by acquiring the lighting time of a specific light color of the traffic light by analyzing data about a video of an area ahead of the vehicle without going through infrastructure equipment.
In addition, patent reference 3 discloses a traffic signal predicting device that forms a traffic light information database by using traffic light information acquired via road-to-vehicle communications, and predicts the time required for the light color of a traffic light to change.